1. Field of the Invention
The field of this invention relates to novel dianhydrides such as bicyclo[4.2.0]octane-7,8-dimethyl-3,4,7,8-tetracarboxylic acid dianhydride (1) and bicyclo[4.2.0]octane-2,5-diphenyl-7,8-dimethyl-3,4,7,8-tetracarboxylic dianhydride (II) and novel polyimides and copolyimides prepared from these dianhydrides and diamines. These novel polyimides and copolyimides are useful in preparing molded articles, fibers, laminates and coatings.
2. Background
British Pat. No. 570,858 discloses various processes for making fiber forming polymers. It is clear that neither the novel dianhydrides nor the polyimides and copolyimides prepared therefrom, which are useful as moldings, fibers, laminates and coatings, have been contemplated in the prior art.
The general objective of this invention is to provide novel dianhydrides. A more specific object is to provide novel polyimides and copolyimides based on I, II and diamines or mixtures of diamines. Another object is to provide copolymers based on either I or II and another dianhydride.
We have found that novel polyimides can be formed by reacting dianhydrides of the following structure: ##STR1## wherein Z is a hydrogen or benzene radical with diamines. These novel dianhydrides are prepared by a photocycloaddition reaction between dimethylmaleic anhydride and either 3,6-diphenyl-4 cyclohexene-1,2-dicarboxylic anhydride or cis-4-cyclohexene-1,2-dicarboxylic anhydride. Both I and II react readily with the diamine to form a high molecular weight polyimide or copolyimide. In the novel process aliphatic, cycloaliphatic, araliphatic and aromatic diamines can be polymerized with I or II in the melt to form high molecular weight polyimides and copolyimides.
Our process for the manufacture of the novel polyimides and copolyimides comprises reacting about equal molar amounts of the dianhydride with a primary diamine or a mixture of primary diamines. The molecular ratio of the dianhydride to the primary diamine may be in the range of 1.2 to 1 preferably in the range of 1 to 1. In suitable method, the reaction is conducted as a batch reaction at a temperature of about 130.degree. to 300.degree. C. for a period of about 2 to 8 hours in a nitrogen containing organic polar solvent such as N-methyl-2-pyrrolidinone, N,N-dimethylacetamide or pyridine. Either I or II can be replaced by another dianhydride up to 70 mole percent.
The other dianhydrides are characterized by the following formula: ##STR2## wherein R' is a tetravalent organic radical selected from the group consisting of aromatic, aliphatic, cycloaliphatic, heterocyclic, combination of aromatic and aliphatic, and substituted groups thereof. However, the preferred dianhydrides are those in which the R' groups have at least 6 carbon atoms wherein the 4 carbonyl groups of the dianhydride are each attached to separate carbon atoms and wherein each pair of carbonyl groups is directly attached to adjacent carbon atoms in the R' group to provide a 5-membered ring as follows: ##STR3## The preferred dianhydrides, as recited above, yield upon reaction with the diamines polyimide structures having outstanding physical properties. Illustrations of dianhydrides suitable for use in the present invention include: pyromellitic dianhydride; 2,3,6,7-naphthalene tetracarboxylic dianhydride; 3,3',4,4'-diphenyl tetracarboxylic dianhydride; 1,2,5,6-naphthalene tetracarboxylic dianhydride; 1,2,3,4-cyclopentane tetracarboxylic dianhydride; 2,2',3,3'-diphenyl tetracarboxylic dianhydride; 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride; 3,4-dicarboxyphenyl sulfone dianhydride; 2,3,4,5-pyrrolidine tetracarboxylic dianhydride; 3,4,9,10-perylene tetracarboxylic dianhydride; bis(3,4-dicarboxyphenyl)ether dianhydride; ethylene tetracarboxylic dianhydride; 3,3',4,4'-benzophenonetetracarboxylic dianhydride; bis(3,4-dicarboxyphenyl)sulfide dianhydride; bis(3,4-dicarboxyphenyl)methane dianhydride; 1,4,5,8-naphthalenetetracarboxylic dianhydride; tricyclo[4,2,2,0.sup.2,5 ]dec-7-ene-3,4,9,10-tetracarboxylic dianhydride; 3,6-ethenohexahydropyromellitic dianhydride; cyclobutane-1,2,3,4-tetracarboxylic dianhydride; and 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride. The polycondensation can also be carried out as a continuous process. The polycondensation can suitably be carried out at a temperature of 130.degree. C. to 300.degree. C., preferably at a temperature of 180.degree. C. to 250.degree. C. The novel polyimides of this invention have the following recurring structure wherein R is a divalent aliphatic or aromatic hydrocarbon radical and Z is a hydrogen or benzene radical: ##STR4## The radical R may be divalent aliphatic hydrocarbons of 2 to 18 carbon atoms or an aromatic hydrocarbon from 6 to 20 carbon atoms, or an aromatic hydrocarbon radical containing from 6 to 10 carbon atoms joined directly or by stable linkage comprising --O--, methylene ##STR5## radicals. The radical R is derived from aliphatic, araliphatic or cycloaliphatic diamines such as ethylenediamine, propylenediamine, 2,2-dimethylpropylene diamine, tetramethylene diamine, hexamethylene diamine, octamethylene diamine, nonamethylene diamine, decamethylene diamine, dodecamethylene diamine, 4,4'-diaminodicyclohexylethane, xylylene diamine and bis(aminomethyl)cyclohexane. Suitable aromatic diamines useful in Applicant's process include para- and meta-phenylenediamine, 4,4'-oxydianiline, thiobis(aniline), sulfonylbis(aniline), diaminobenzophenone, methylenebis(aniline), benzidine, 1,5-diaminonaphthalene, oxybis(2-methylaniline), thiobis(2-methylaniline), and the like. Examples of other useful aromatic primary diamines are set out in U.S. Pat. No. 3,494,890 (1970) and U.S. Pat. No. 4,016,140 (1972) both incorporated herein by reference. The preferred diamines are hexamethylene diamine, dodecamethylene diamine and 4,4'-oxydianiline.
In some cases the polyimide or copolyimide may be further polymerized under "solid state polymerization" conditions. The term solid state polymerization refers to chain extensions of polymer particles under conditions where the polymer particles retain their solid form and do not become a fluid mass. The solid state polymerization can be carried out below the melting point of the polyimide and can be conducted in several ways. However all techniques require heating the ground or pelletized polyimide below the melting point of the polyimide, generally at a temperature of about 175.degree. C. to 300.degree. C. while either sparging with an inert gas such as nitrogen or operating under vacuum. In cases where the polyimides have a low melt temperature, they can be polymerized in the melt under vacuum in thin sections or using thin film reactors known in the art.
Injection molding of the novel polyimides and copolyimides is accompanied by injecting the polyimides or copolyimides into a mold maintained at a temperature of about 25.degree. C. to 150.degree. C. In this process a 20 second to 1 minute cycle is used with a barrel temperature of about 125.degree. C. to 350.degree. C. The latter will vary depending on the Tg of the polymer being molded.
The novel polyimides and copolyimides have good thermal properties and can be molded into useful articles or formed into fibers, films, laminates or coatings. Infrared spectra of the polyimides have confirmed the polyimide structure.
Analysis of the polyimide by thermal gravimetric analysis shows excellent stability. Glass transition temperature Tg of the polyimide varied with the particular diamine used as shown in the Examples. Values range from a Tg of 60.degree. C. to 180.degree. C.
Diamines with the amino groups attached directly to the aromatic ring are suitably polymerized with the I or II by solution condensation in organic polar solvents. These include N,N-dimethylacetamide, N-methyl-2-pyrrolidinone, N,N-dimethylformamide, pyridine and the like. We have found that the polyimides and copolyimides of this invention are improved by the addition of reinforcing material. Suitably about 25 to 60 percent by weight of glass fibers, glass beads or graphite or mixtures of these can be incorporated into the polyimides and copolyimides. Any standard commercial grade fiber, especially glass fibers, may be used. Glass beads ranging from 5 mm to 50 mm in diameter may also be used as reinforcing material. Injection molding of the novel glass filled polyimide is accomplished by injecting the polyimide into a mold maintained at a temperature of about 50.degree. C. to 150.degree. C. In this process a 25 to 28 second cycle is used with a barrel temperature of about 125.degree. C. to 350.degree. C. The injection molding conditions are given in Table 1.
TABLE I ______________________________________ Mold Temperature 50.degree. C. to 150.degree. C. Injection Pressure 15,000 to 19,000 psi and held for 1 to 3 seconds Back Pressure 100 to 220 psi Cycle Time 25 to 28 seconds Extruder: Nozzle Temperature 125.degree. C. to 350.degree. C. Barrels: Front heated to 125.degree. C. to 350.degree. C. Screw: 20 to 25 revo- lutions/minute ______________________________________